Field of the Invention
This invention pertains generally to substance abuse research systems, and more particularly to substance inhalation systems and methods for test animals.
Description of Related Art
The destructive effects of alcohol and drugs such as THC (tetrahydrocannabinol), cocaine and other stimulants are vast and well known and have led to the creation of the National Institute on Drug Abuse (NIH) and National Institute of Alcohol and Alcohol Abuse (NIAAA). Over the years, investigators funded by NIH and NIAAA have developed several systems for the delivery of drugs and alcohol which include presenting the drug as a liquid diet; injecting alcohol via gastric, intraperitoneal or intravenous routes; and by exposing test subjects, e.g., rodents, to drug and alcohol vapors. Each method has advantages and drawbacks that are abundantly discussed in the available literature. However, one significant problem that has consistently plagued research is the difficulty in reaching predictable blood levels (BLs) of drug and alcohol and, if desired, maintain them within given values. Injections of a specific concentration of drugs or alcohol can be used but this procedure is very stressful unless the animals are equipped with indwelling permanent cannulae. This requires skillful surgical training. Gavage via the forceful placement of a special tube into the esophagus can be done but is also very stressful, particularly if it is used repeatedly. Also both methods (injections and gavage) induce rapid peak BLs followed by the disappearance of drugs and/or alcohol from the circulation. They cannot be used to maintain constant BLs over time. Feeding drugs or alcohol in the diet presents the advantage of voluntary drug intake but does not provide the investigator with significant control over the amount of drugs or alcohol consumed, and consequently BLs are not consistent.
All of these problems have been critical barriers in drug and alcohol research. For this reason, many investigators have turned to delivery of drugs and alcohol through vapors. This method, as presently used, allows preparation of animals with more predictable BLs than the diet. However, it has its own inherent technical obstacles. For example, presently available drug and alcohol vapor chambers systems are very large because they can contain up to fifteen test subject cages. These chambers typically require an entire dedicated room and are built “in house”, which makes the data collected completely unique to each system. The results from such individualized systems cannot be compared to results from other research facilities or universities as they are all different systems. Therefore, it is often difficult to achieve reproducible results from chamber to chamber and from experiment to experiment. Another major obstacle with the current individual systems is that they are built to house many animals together. This requires the investigator to open the entire system to remove one animal, for example to check its BAL. This unavoidably destroys the balance in the system, which requires time to return to equilibrium. Additionally, the handling of the animal causes stress hormones such as corticosterone to be released, which can interfere with the outcome of the results. Finally, not only is the initial cost of building these systems very high, the expense to run them is also high given that they require a full-time employee dedicated to their maintenance.
U.S. Pat. No. 7,252,050 of Cole describes a portable substance inhalation system which has separate inhalation chambers on shelves of a housing supported on a wheeled cart, and a single vapor delivery system mounted on the cart and connected to the inhalation chambers by delivery lines. This overcomes some of the limitations in prior drug and alcohol delivery systems for test purposes.